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Full text of "LATEST CIVILIAN V/STOL AIRCRAFT PROJECTS OF HAWKER SIDDELEY AVIATION, CONTINUATION FROM FR6/71"

NASA TECHNICAL TRANSLATION NASA TT F-14,629 



LATEST CIVILIAN V/STOL AIRCRAFT PROJECTS 
OF HAWKER SIDDELEY AVIATION 
(Continuation from FR6/71) 



T. K. Szlenkier 



(NASl-TT-F-14629) LATEST CIVILIAN V/SfOL N73- 10034 

AIRCRAFT PROJECTS OF HAWKER SIDDELEY 

AVIATION, CONTINDATION FROM FR6/71 T.K, 

Szlenkier (Scientific Translation Service) Unclas 

Nov. 1972 22 p CSCL OlB G3/02 46161 



Translation of: "Neueste zivile V/STOL-Flug- 
zeugprojekte von Hawker Siddeley Aviation", 
Flug Revue/Flugwelt International, July 1971, 
pp. 35 - 38 and 43 - 46. 




NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D. C. 20546 NOVEMBER 1972 



Reproducod b/ 

NATIONAL TECHNICAL 
INFORMATION SERVICE 

U S Department of Commerce 
Springfield VA 22151 



J 



LATEST CIVILIAN V/STOL AIRCRAFT PROJECTS 
OF HAWKER SIDDELEY AVIATION 
(Continuation from FR6/71) * 

T. K. Szlenkier** 

ABSTRACT. The latest civilian V/STOL aircraft are 
examined. It is found that such aircraft are more econo- 
mical and convenient in short air flights, require lower 
capital investments compared with other systems, and 
have less influence on the environment . 



CONCLUSION OF PART ONE 

Only a relatively simple flapj' for which the air stream came from the 
inside was investigated by HSA in the year 1970. The area loading for the -^ 
design was 390 kg/m2, and a take-off distance of 600m is required. The 
installed thrust/weight ratio is 0.4 and the by-pass ratio of the forward 
engines is 3.0. The aircraft weight, initial costs and direct operational 
costs were greater than for STOL aircraft having fan-lift engines. 

PART TWO: MECHANICAL FLAPS 

^ I 
The STOL aircraft with mechanical flaps according to Figure 19 hajs four 

forward engines with a high by-pass ratio. These engines are derived from the 

Rolls-Royce RB 410. A gas generator, developed from the M 45 H powers a blowerj 

having a reversed blade inclination and a by-pass ratio of almost ten through 

a gear. In order to install such large engines' under the wing, a shoulder 

covering arrangement is necessary. 



*** 



Translator's note: Part I available in English as NASA TTF 14,619^, 

Hawker Siddeley Aviation Ltd. 
*** 

Numbers in the margin indicate pagination in the original foreign texjt. 

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In this design, the effects of the jet flaps with air coming from the 
outside were Intentionally avoided and the engines were suspended from long 
posts, in order to have predictable and conventional handling characteristics 
in case an engine failed. If the outer jet flap effect is taken advantage 
of to its fullest extent, there are large changes in the lift distribution 
along the wing if an engine falls. This requires very complicated control 
systems in order to satisfy the aircraft handling requirements. 

In order to obtain a high lift, an almost straight wing with a high 
aspect ratio is used, which has wing loading during take-off of only 320 kg/m . 
The wing has an extendable forward wing, slot|ted Fowler flaps and a crossed| 
directional rudder. The maximum velocity characteristics are limited in this 
designjand the cruise Mach| number is limited to 0.70. However, because of 
the selected " engines" with the large by-pass ratio and the reversible| 
blowers , it would not be possible to have a velocity which is much higher. 

The design has the advantages of improved flight path control and thrust 
braklng.| However, there are restrictions due to blower strength and blade 
profile. 

Although |the design with mechanical flaps has tjhe advantage of simplicity, 
the large weight of the large wings and the reduced productivity due to the 
limited cruise velocity bring about a;n Increase in the indirect operational 
costs amounting to 10%, compared with the aircraft having four lifting engines. 

SUMMARY 

The first investigations on jet propelled STOL aircraft j which were 
terminated in 1970, showed that air|craft having fan lift engines were| superior 
with} respect to economy of operation compared with solutions having mechanical 
flap systems and central flaps in which the air comes from the inside. 
Compared with the aircraft having mechanical flaps, the direct operational 
costs are about 10% lower, and compared with the aircraft having flaps from 
which the air comes from the inside, they are about 4% lower. Neverthless, 
it is necessary to perform additional investigations of complicated flap 
systems, because such designs could be more economical compared with the 
simpler systems. 




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The aircraft with lifting engines have a number of other advantages, 
which will be considered later on. There are indications that the STOL 
aircraft with lifting engines, as suggested in 1970, can be improved even 
further. These indications led to the present STOL suggestion, which will 
be discussed in the next paragraph. 

6. STOL COMMERCIAL AIRCRAFT WITH FAN JET ENGINES, DESIGN STUDY NO. 147 (1971). 
6.1 General Description 

For some time it] has been known (see also Section 4.6), that jet 
interaction during forward flight are|' not the same for all engines because of 
the lifting engines located in thejpods, such as in the HS141-16 or the 
STOL aircraft according to Figure 19. Instead] this depends on the position /36 
of the engines in front of or behind the wing. In general there is a loss 
in lift if the engines are located ahead of the wingj and there is an increase 
in the lift if they are located behind the wing. The order of magnitude of 
this effect decreases as the distance of the wing increases. Model experiments 
of the STOL aircraft mentioned above in theRollspRoyce RB 410 of HSA showed 
(Figure 7 ) the aerodynamic effect of jet interaction is more advantageous 
for lifting engines located at the rear than could be expected. 

For these reasons, a design was assumed (Study No. 147), as shown in 
Figure 22. This aircraft has only two lifting engines in half pods behind 
the wing. Because of the necessity of trimming the pitch moments produced /37 
by the lifting] engines located behind the center of gravity by raising the 
tail, it is not possible to obtain the entire gain caused by interference. 
Nevertheless, a valuable improvement| is obtained in comparison with earlier 
STOL designs with lifting engines . 

The Study 147 STOL aircraft satisfied, the requirements in Table 2 
and Table 3l except that the descent rate during approach was increased. 
The aircraft design is conventional except for the small half pods. One 
lifting engine is installed in each of these pods. Other characteristic 
features arejthe fact that the wings have a low position and the forward 
engines are installed in a manner similar to the HS 141-16 or HS 141-12 
V/STOL projects. 

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projects. However, they belong to an earlier construction series] and have 
a lower thrust/weight ratio. The lifting engine installation is similar to 
that of the HS 141-16. However, the deflection range was increased in order 
to increase the relative lifting thrust contribution during the accelerating 
and braking phases of STOL operation. Quiet "engines" are located under the /38 
wing. Outer jet flap effects are avoided by means of relatively long supports. 
The design cruise Mach number-| is 0.75. The high lift devices consist of forward 
wings which can be extended over the entire span as well as large slotted 
mechanical Fowler flaps. 

The control around the yaw axis is done by means of a rudder and 
perforated spoilers in front of the flaps. If there is a failure in the 
lifting engines, trimming can be done with the rudders alone, and there will 
still be available sufficient reserves for control around the roll axis. If 
the forward engines fail, a double hinge side rudder can be used to compensate 
for it. The design also can withstand 25 knot cross-wind components. 

The fuselage has the comfort level of coach class and there are five 
seats next to each other. One hundred passengers can be seated with a seat 
distance of 34 inches. The baggage is located in two compartments below the 
floor,] and there is good accessibility from the side. 

6.2 WEIGHTS AND PERFOEMANCES . 

In order to transport 100 passengers (9100 kg payload) over two distance 
segments of 370 km each, the STOL design take-off weight is 52600 kg. The 
operational empty weight is 36,300 kg. The 2x270 flight distance assumed in 
the design was performed at a cruise Mach number of 0.75 at an altitude of 
6100 m. This corresponds to a velocity of 850 km/h. The distance without 
intermediate landing corresponding to this is 980 km. The range with full 
payload can be Increase to 1090 km, if long distance performance is assumed. 
Because of the increased take-off weight from airfields with a length of 750 m, 
the range can be increased up to 2400 km. The maximum inclination angle after 
take-off is 17.5° and the approach angle is 7.5° during landing. 

6.3 NOISE LEVEL 

Due to the noise development of the RB 202-31 lifting engines and the 

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Size comparison 
CTOL. STOL & VTOL airports 



Conventional airport 



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elevated 
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4 storey 



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per annum 



scale I 1 1000 ft 



Fig. 30: Comparison of the airport sizes for CTOL, STOL and VTOL. 

quiet forward engines, the length of the 90 PNdb sound ellipse on the ground 
is 3540 m, and its area is almost two square kilometers (see Figure 24). The 
absorption of the noise by the ground was considered in these estimates. /43 

6.4 SAFETY AND COMFORT LEVEL 

Safety of operation of the STOL aircraft with fan jet engines is provided 
due to the fact that it was designed according to specifications of aviation 
boards such as the ARB, LBA, FAA. Special care must be given to the engine 
performance requirement. However, there are other STOL solutions in which the 



engines make a contribution to the aerodynamic lift. 

In order to operate from airports only 600 m long, relatively high 
accelerations are required. The peak values for operation, however, are 
only relatively higher than for the values specified for take-off and landing 
of the Hawker Siddeley Trident. The pitch positions and rotational rates 



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are also comparable. Therefore, it seems that the planned acceleration and 
pitch position characteristics are quite acceptable for this STOL aircraft. 
Otherwise, passenger comfort is comparable with that of conventional jet 
aircraft, because no design compromises are required with aircraft having 
lifting engines. /44 

6.5 COMPARISONS WITH OTHER STOL DESIGNS 

According to investigations of HSA, the direct operational costs of the 
aircraft according to Study 147 are about 15% below those of the best designs 
with mechanical flaps. Investigations of complicated jet flap designs are still 
incomplete^ however, it is believed that the aircraft with lifting engines will 
be more economical, because the design is hardly restricted by STOL flight 
performance requirements. 

The promising STOL designs also have four engines. This is why the 
ratios of effective installed thrust to weight are comparable. However, in the 
aircraft with fan jet engines, the thrust contribution of the lifting engines, 
(40% of the total thrust) is coupled with the low engine weight, low drag and 
low costs. Other advantages of this design include the following:] /45 

1. It is expected that it will be easier to satisfy the prescribed noise 
restrictions than with jet flap aircraft. According to investigations of 
NASA (SP-259) , considerable difficulties with noise can occur. In the case 
where the flaps receive the air from the outside, the noise production of the 
exhaust jet/flap impingement still represents an unknown. This is also the 
case for the wing slot nozzle when the flap receives the air from the inside. 
The latter operates at a pressure ratio higher than 1.4. 

2. In order to reduce the technical risk, only the aerodynamic high lift 
aids were used which correspond to todays' technology. 

3. The lower wing design can be retained, which is more advantageous for 
supplying the aircraft on the ground. 

4. Only two forward engines are required. The short take-off distance requires! 
no compromise|either in the size or in the installation methods. 

5. The lift can be controlled by thrust modulation of the lifting engines. 

6. STOL as well as V/STOL aircraft with lifting engines have many characteristic 
features. STOL aircraft with lifting engines could be introduced as predecessors 

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for V/STOL aircraft with lifting engines. 

7. RESEARCH AND DEVELOPMENT 

The investigations of the most modem V/STOL aircraft are being 
supported by resjearch programs, in which the V/STOL windtunnel at Hatfield 
(Figure 25) is being used. A number of realistic aircraft models are being 
measured. The sixteen lifting engines on the model of the HS 141-16, each 
having a diameter of 15 cm, are operated with compressed air (Figure 26) . 
The STOL model with lifting engines (Figure 27) , which is being tested in 
the same wind, tunnel J has four 10 cm diameter ejectors to simulate the lifting 
engines. Other models have been tested in the high velocity and extremely 
low velocity wind tunnels! in Hatfield, in order to determine the conventional 
aircraft characteristics and to obtain an estimate of the effectiveness of the 
high lift devices. 

In addition to the wind tunnels, | there are| experimental set-ups which 
have been built, in order to determine the static jet interferences and the 
noise. A 30 cm diameter blower, operated by an air turbine, simulates the 
RB 202. fan. It is used for noise measurements under the most varied| 
conditions, in order to determine the effect of its installation on the cross- 
wind, i.e. (see Figure 28). 

Flight performance and contol problems as well as aircraft control 
near the airport are being investigated in Hatfield in a flight simulator 
(Figure 29) . The simulator is now being modified in order to obtain a moveable 
flight deck area, a digital computer and an improved visual representation. 
Over thirty test pilots of HSA, of the RAE, of the Domier AG, of the BEA and 
of the KLM have participated in the evaluation of the HS 141. Close cooperation 
exists with the Royal Aircraft Establishment in Farnborough and Bedford, where 
research programs complement those of HSA in many ways. In spite of these 
activities, there is a pressing need for tests and conventional development, 
which can only be performed on a full scale operational device. This problem 
can no longer be delayed, if additional advances in the area of modem civilian 
V/STOL and STOL profects are desired. 



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8. SOME APPLICATION CONSIDERATIONS 

A comparison of CTOL, STOL and V/STOL aircraft (see Figure 30), which 
all have the same capacity, showed that a great deal of space can be saved 
by STOL and V/STOL systems. As Figure 24 already shows, the 90 PNdb noise 
zone is considerably smaller for a 100 seat V/STOL aircraft with new technology 
engines than for a STOL aircraft with a 600 m landing field. Nevertheless, 
we may argue that a noise zone at the 90PNdb limit for STOL operation and 
having a size of about 2 km^ can be found in most large cities, either near 
ports or over large railroad freight yards. 

Figure 31 shows VTOL airports of various capacities. The largest one 
is obtained by modification of a STOL aircraft having a single 600 m runway, 
which,lhowever,|would have limited capacity for STOL operation. Therefore, 
if an STOL system is to be the predecessor to the VTOL system, an infrastructure 
would be available which would provide a large increasing capacity when VTOL 
operation is introduced later on. This increasing capacity can also be 
tolerated by the flight controllers , because VTOL has a greater flexibility 
due to the additional approach and landing paths (i.e., the operation is 
greatly independent of wind direction and turbulence) . This leads to a better 
efficiency in the use of the air space. Figure 32 shows the separation of the 
various aircraft traffic types, which can be obtained by VTOL operation. 

9. V/STOL ECONOMY 

The economic advantages of V/STOL are summarized in Figure 33. Here 
it is shown that the relatively high procurement costs of the STOL and VTOL 
aircraft are| equalized by the increased productivity, which reduces the direct 
operational costs. These come about by time savings during take-off and 
landing, as well as on the ground because of the reduced taxiing distances. /46 
If the same indirect operational costs are assumed as for conventional 
aircraft operation, the total operational costs (direct and indirect) are 
only slightly above those for CTOL. If we also include the low costs for 
arrival and departure to and from the airport, one finds that the total costs 
are almost the same for all systems. However, VTOL and STOL offer considerable 
time savings. Considering the fact that the noise zone for STOL is larger 

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than for VTOL (see Figures 24 and 33) , it can be assumed that STOL airports 
will have to be located farther away from points where the demand exists 
than Vertiports. This explains the further reduction in the travel time 
on the- ground in the favor of V/STOL. . Neverthele ss, . even. the, smallj 
time savings for STOL are considerable. If we now assume that "time is money", 
and we assume that the average traveler will account for his time at a rate of 
about 10.0 DM per hour (of course the rate would] have to be higher for 
businessmen) , effective total travel costs could be defined which, for a 
distance of 560 km, would be about 10% lower for V/STOL and about 5% lower 
for STOL than for CTOL. These estimates do not even consider the delays 
caused by the over-billed air space and the associated higher costs of CTOL, 
as well as the time savings for STOL and VTOL. Also the increased aircraft 
use has not been considered. 

10. CONCLUDING REMARKS 

The main arguments in favor of STOL and V/STOL systems equipped with] 
fan lift engines are the following: 

— Considerable improvement in short distance air traffic due to economy and 
convenience, 

— lower capital investments compared with other systems, 

— social-political reasons because of reduced influence on the environment. 

It seems that aircraft with fan lift engines are the optimum solution 
for both STOL and V/STOL. The required state of the art has been reached 
in Europe. Nevertheless,] there are considerable difficulties associated with 
convincing the public, the government officials and airline officials that 
VTOL really does have advantages as promised. For this reason, decisions 
are being delayed and the required funds for development are not being 
provided. If this situation persists, advances will only be made by a 
stepwise evolution. STOL would then represent a logical intermediate step, 
because STOL is simpler and can be operated more economically using the 
existing infrastructure than can be done with VTOL. 

As the integration of western Europe progresses, it is important 
to make sure that the new STOL and VTOL systems will be oriented according 
to a European solution and not according to a national solution. This 



20 



requires early cooperation of all affected agencies , in order to avoid 
diajplication which would occur in an uncoordinated and separate development. 

The enormous possibilities which STOL and VTOL offer to Western Europe 
should be pursued immediately. This would mean an aircraft such as shown in 
Figure 34 could be built within the next decade. 

11. POSTSCRIPT 

The author would like to thank the directors of Hawker Siddeley Aviation 
Ltd. for permission to publish this article. He thanks his colleagues in 
Hatfield for their support. The opinions and statements are those of the 
author and are not necessarily the official policy of the firm. /35 

TADEUSZ KAROL SZLENKIER 

Tadeusz Karol Szlenkier is Deputy Chief Project Engineer at Hawker 
Siddeley Aviation in Hatfield. He has a Bachelor of Science and Master of 
Science (Engineering) degrees from the University of London. Szlenkier was 
bom in 1917 as the son of Polish parents in Switzerland and went to school 
in Warsaw. He obtained his technical education at the Warsaw Polytechnical 
Institute and London University. During the Second World War he was in the 
Polish Air Force. He was in the Royal Air Force from 1940 to 1945. Szlenkier 
spent two years in Soviet prison camps, before he joined the RAF, where he 
was a senior pilot and fighter pilot in northwest Europe. From 1949 to 1952, 
Szlenkier gave lectures on mechanical engineering at the Polish University 
College in London. From 1952 to 1959, he worked as a senior aerodynamicist 
and thermodynamicist at de Havilland Aircraft Company in England, Canadair 
Ltd. in Canada and Lockheed-Georgia in the U.S.A. In 1959, Szlenkier then 
went to Hawker Diddeley Aviation in Hatfield, where he specialized in the 
area of V/STOL. From 1964 to 1965 he represented HSA at Dornier AG in 
Immenstaad and was a member of the directorate of joint projects during the 
development of the Do 31. 



Translated for National Aeronautics and Space Administration under contract 
No. NASw 2035, by SCITRAN, P. 0. Box 5456, Santa Barbara, California, 93108 



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